CBAT
It appears that only 40 Copenhagen cards were issued between 1914 and the beginning of the IAU's CBAT in Uccle in 1920, most of which were typeset and printed, but some of which were handwritten (and possibly then mimeographed onto cards?). Curiously, there appears to have been no official name for the cards (such as "Circular") printed on the cards themselves. When the IAU established its new CBAT at Uccle in 1920 (apparently bypassing Strömgren because of his known friendship with the Germans at Kiel in that very political post-war era), and the first series of IAU Circulars were published there (in larger paper form, not as postcards), Strömgren essentially ceased publishing his postcard circulars. However, more than two-dozen additional COCs were published after the CBAT moved from Uccle to Copenhagen, curiously. The Kiel connection is seen at the top of the COCs issued after 1920, where the title "Kieler (Astronomische) Zentralstelle/Zweigstelle Kopenhagen" appears -- and where there is a distinguishing between the IAU Central Bureau and the original Central Bureau at Kiel that was transferred (temporarily) to Copenhagen where it was considered a "twin" bureau of the Kiel bureau. The world wars prevented Germany from being admitted to the IAU until 1951, explaining why the IAU did not accept Kiel (or, for the first three years, Copenhagen) as its Central Bureau, and why Kiel insisted on recognizing a non-IAU Central Bureau for years after the IAU started.
Some of the information on Uccle's IAUC 1 appeared on COC 39, and COC 40 contains some of the information that appears on IAUC 2. Then there was a break of several months before COC 41 was issued, containing largely the information that appears on IAUC 5 in July 1920. At that point, there was a long break, with no COCs issued from Copenhagen for over two years. In that time span, the IAU had decided after all to move the CBAT from Uccle to Copenhagen under Strömgren's able direction. Strömgren's assistant with the Central Bureau at that time was Julie M. Vinter Hansen, who would become CBAT Director upon Strömgren's death nearly three decades later. Curiously, five COCs were published during six months from late 1922 into early 1923 (after the new series of IAUCs began at Copenhagen), and all the last five COCs were edited by Vinter Hansen and issued in German -- all corresponding to IAUCs issued at the same time in French, edited by Strömgren! But these COCs appear to have been somewhat random: COC 42 contains most of what is on Copenhagen IAUC 1; COC 43 contains the same text as appears on IAUC 2; COC 44 contains most of what is on IAUC 5; the first two items on COC 45 appeared also on IAUC 9; and COC 46 contains the same text as appears on IAUC 13. The COCs continued to be published in German and edited by Vinter Hansen (with one exception -- COC 48, by Strömgren) through number 66 on 1926 Jan. 26; there was then a lapse of nearly four years (to COC 67 on 1929 Dec. 24), with the final four COCs (still in German) signed by Strömgren -- COC 70 being the final such circular on 1930 June 7.
COCs
The COCs are being made available here as scanned jpeg images, as time permits.
We thank Emma Palmqvist (Librarian for Astronomy and Geophysics, Neils Bohr
Institute, Copenhagen) for sending photocopies of these cards. The cards
were all assembled into a single bound volume at the Copenhagen Observatory
Library with no title page, but with the words "KBHVNS. OBS. CIRKULAERER
1914-1930" on the spine (the Library's set of IAUCs were also bound
into books, the results of which can be seen in the scans of many of those
cards on our
scanned-IAUCs webpage).